Seven isolates of the potato virus Y collected from various sources in the state of São Paulo, Brazil, were compared in their morphology with the typical potato strain The preparations were made by the exudate or dipping methods and examined in a Siemens Elmiskop I electron-microscope Elongated, flexible virus particles found in the preparations of all isolates did not differ significantly from the normal length, about 730 mm, reported for the potato Y virus in other places. One of the isolates, designated as YP (normal length 723.8 mμ.) showed a tendency to be slightly shorter than the average and two others, YW and YWRio (normal lengths 737 mμ and 737.8 mμ) were slightly longer than this value. The similarity in the morphology of all isolates is considered as satisfactory evidence that they are all related.